This invention relates to a system for cleaning a dry process vacuum pump and, in particular, a system using a high pressure gas cleaning purge to clean a dry process vacuum pump on a Czochralski-type (CZ) crystal grower.
In the semiconductor industry, semiconductor crystals are typically grown in a CZ crystal growing furnace. During the crystal growing process, the chamber of the CZ furnace is typically maintained at various levels of vacuum.
To maintain the reduced pressure in the CZ furnace, a vacuum pump is run continuously during the crystal pulling process. The vacuum pump is subjected to substantial quantities of silicon oxide dust, a byproduct of the process inside the CZ furnace. In the past, oil-sealed vacuum pumps were used. However, the oil present in an oil-sealed pump is a potential source of vacuum and process gas contamination. Additionally, maintaining filters and exhaust oil-mist separators proves to be a significant expense.
To avoid the problems associated with oil-sealed vacuum pumps, some manufacturers use a dry pump as the vacuum pump on a CZ crystal grower. In contrast to the oil seals used in an oil-sealed pump, a dry pump relies on extremely close tolerances between its rotors and stators to provide the necessary seals within the pump. The absence of oil in a dry pump avoids the above mentioned problems associated with an oil-sealed pump. However, the extremely small gaps between the rotors and stators of a dry pump can be filled by the silicon oxide dust, resulting in increased current load on the pump motor. Allowed to continue unchecked, this increased load may result in overload of the motor, tripping a circuit breaker and causing an abort of the crystal growing run. Aborts are extremely expensive due to the associated production down time and product loss.
FIG. 1 shows a dry vacuum pump 10 having a vacuum pump inlet 50 connected to a crystal grower 30 by way of a vacuum pipe 40 and a booster pump 20. The gases drawn from the crystal grower 30 by the dry vacuum pump 10 are exhausted to a building exhaust system 70 by way of a vacuum pump exhaust 60. Traditionally, dry pumps used to pump harsh processes or particulate-laden gases use a "cleaning cycle" at some point before, during, or after a run. The pump cleaning system shown in FIG. 1 circulates atmospheric air 90 through dry vacuum pump 10 in an effort to remove silicon oxide dust deposited in the dry vacuum pump 10 during the crystal growing process. During the cleaning process, cleaning cycle valve 80 is opened and the dry vacuum pump 10 draws large amounts of atmospheric air 90 through the dry vacuum pump 10. During the crystal growing process, cleaning cycle valve 80 is closed.